An antistatic wrist strap is a useful thing to use when handling static sensitive devices like computer cards and ram, or static sensitive chips. Touching the computer case is only useful if it is plugged in to the mains with a grounded pin. If it is not, you do not get rid of any static charge buildup. To make your own, you need to have metal contacting your body through a metal bracelet. You then wire this bracelet through a 1 Megaohm resistor to a crocodile clip. YOU MUST USE THIS RESISTOR just in case you accidently make contact with a live wire. The crocodile clip is then clipped to the earth or ground point.